I'm trying to describe the costs of multitasking. Here's what I've got so far:
There are three parts to multitasking:
- Stopping the work you're doing. The stopping cost is the time it takes to mark your place, save your work, etc. You haven't stopped thinking about what you're doing, but when you stop to take a phone call or answer a question, there's a stopping cost. If you're in flow, this is surprisingly high.
- Swapping out what you're working on. The swapping out is the act of clearing your mind of the work you'd been doing so you have room to swap in the new work. If you were in flow or concentrating deeply, this can take anywhere from 5 minutes to 30 minutes. Sometimes, it takes me even longer.
- Swapping in the new task. The swapping in depends on the complexity of the work and how long it's been since you last touched the task. The more complex and the longer the time since you last touched the task, and the more people you have to talk to, the longer it takes.
I don't know how to give ballparks for each of these. Certainly, for some tasks, it's fairly trivial. If I'm organizing a normal weekday dinner, my swapping in/out is very fast, because there's little knowledge associated with each task. But now when I write chapters of a book (or back when I was writing code,) the costs can be very high, because the knowledge in my head is not yet written down. For me, the stopping the work is defect-inducing. Unplanned interruptions help me make defects. So does the swapping back in, if it's been a long time since I last worked on this task.
Did I miss anything?